First of all, welcome!
What to sell? anything and everything. If you want to specialize, you should...but keep in mind that it will require that you do a lot of advertising outside of shapeways. Something to keep in mind with shapeways buyers is that they are modelers(generally) that are (generally) capable of creating their own stuff...bluntly: they dont need you, or me, or any other shops.
Of course, that is very general. The reason I put it that way is because people buy things that they cant buy at the store. So you really have to put your thinking cap on for new designs and ideas.
Popular items that I have seen are puzzles, characters, jewelery and of course anything co-creator.
Pricing is tough...I have yet to figure it out. Because of volume sales, its tough to say "cheaper is better" because you may only sell 5 models, and those 5 buyers maybe have been willing to pay $100 when you only charged them $25, you just lost potential income. Here is a link to a forum post where i tried to gather some of this info:
https://www.shapeways.com/forum/index.php?t=msg&th=2351&a mp;start=0&S=395f5a179271c35eff0b17363d339bca
You can find info on material properties under the Materials Page (Support>Materials) Also, expect to do some printing of your own to verify your models - people are more willing to buy something that is guaranteed to work when they get it, especially if they dont understand the process.
My personal feelings:
Keep in mind that even though you plan on making a shop (to make money) we are still a community. Therefore, in my opinion, rating down your competitors models or somehow degrading another member/members creation is unaccaptable in a community. We all help each other.
Good luck!
and dont forget to advertise outside of shapeways! Facebook and Twitter help a lot!
Oh, and dont forget to check out my shop!
Jake
PM me if you need anything
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Jake Drews
JakeDrews.Com